I alway carry the following
X2 spare inner tubes
Puncture repair kit
Spare chain links and quick links
cable ties
batteries
Spare Light (head band mounted)
X2 Multi tools (each have different tools on them)
Tyre levers
Mini Pump
water bottle (attached to bike)
Disposable rubber gloves (X1 pair)
Mobile phone
£20 in cash
Spare Gilet
Light water proof jacket
Personal details in wallet (name address next of kin. phone numbers)
all packed away neatly into my Altura quick release seatpost mounted bag
That's every time I use the bike, no matter what distance, in winter I'll carry and extra pair of gloves (so I can switch from long fingered to short) and my trusty Camelbak and food on long distances.
Here's a tip. One £20 note is a lot lighter than twenty £1 coins.